Jumpin on the P-38 bandwagon

[Seeker]

Some A´H fuel to the fire....'
Ïf it's accepted that *type* could be seen at relativly long raange (Spit/Fw/P38) bit *marque* was hard to see, what implications does that have for an icon system?

[HoHun]

Hi Bolillo_loco,

>he states that the second LO series of 38L production batch used this power as standard. not the first 38L series which used the same power limitations as the J series.

Would that be the P-38L-5-LO and the P-38L-15-LO respectively? I'm not quite sure about the exact designations.

>Tony levier states that mach .72 was completely safe with dive flaps for the P-38 and many manuals and pilots stated that recovery was effortless with dive recovery flaps. also dives from 20,000 ft are said to have been no problem for the 38 with or with out flaps. the P-51 series is stated to have a max safe dive speed of mach .75, is there that much of a difference?

The corresponding number for P-38 with dive brakes and P-51 were Mach 0.68 and Mach 0.75 respectively. This was the placarded maximum where the airplane was still controllable. You could exceed this Mach number, which in both aircraft would virtually freeze the controls, and in the P-38 induce a heavy nose-down trim.

Mach 0.72 might have been safely attainable with trim properly set before the dive by an experienced test pilot following instructions from the company engineers, but the much lower limit in the pilot's manual made sense since if you exceeded Mach 0.68 in the heat of combat, results could be catastrophical. It wasn't as bad in the P-51 - diving to lower altitudes, the constant true air speed would translate into decreasing Mach numbers, so it would be possible to pull out again at lower altitude.

Eric Brown, a British test pilot working for the Royal Aircraft Establishment which was leading in high speed research during WW2, refers to "maximum safe Mach number" and "maximum tactically useful Mach number".

Maximum tactically useful for the P-38 versus the P-51 was Mach 0.68 at best, versus Mach 0.75 respectively. Maximum safe was Mach 0.72 versus Mach 0.86 (quoting Gripen's Borsodi number).

Another Mach number related topic that Gripen first mentioned in another thread is that at increasing angles of attack, the critical Mach number dropped. The result is that manoeuvrability suffered - and it was worse for the P-38 at great altitudes than for the P-51.

Regards,

Henning (HoHun)

>posted 12-07-2001 12:03 AM

[HoHun]

Hi Hilts,

>Documentation of 64" of manifold pressure can be found in the Lockheed charts in the article "Der Gabelschwanz Tuefel" by Dr. Carlo Kopp, on C.C Jordan's website "Planes and Pilots of World War II".

Thanks, I found it. I had thought you might have a primary source, though, like the manufacturer's engine power charts we have seen posted here for the Jumo 213 or BMW801 engines.

Here's a quote from Kopp's article:

"The two Allison V-1710F-30 V-12s had a 5.5 in. bore and 6.0 in stroke, providing a compression ratio of 6.5. These drove Curtiss Electric constant speed props via a 2:1 reduction gear, delivering 1,475 HP military and takeoff ratings at 3,000 RPM, or 1,612 HP maximum rating at 3,000 RPM and 60 in. of manifold pressure. Some later engines are described as delivering up to 1,725 HP WEP rating."

His statement regarding the 1725 HP engines - which would indicate the 64" Hg manifold pressure according to the graphs - seems very cautious to me. "Later" could imply that these were engines that weren't incorporated into series production, for example, or even that the quoted top speed graph was only a calculated projection.

>As far as how to deal with the German fighter in a dive while flying the P-38, Lowell said you could roll and pull a G or two and follow any prop fighter in a dive. Heiden never mentioned his maneuver, but said he could tailgate any German plane in a dive flying a P-38J with dive flaps. Heiden also said the the P-38L could do anything as well as the P-51 could, and he flew both of them.

Lowell's tactics limit the speed build-up during a dive, which is a useful manoeuvre of course. If attacking a Luftwaffe pilot who just dives away without having to care about excessive speed build-up, the P-38 will be left behind anyway. That's what Gerald Brown meant by his statement

"Early on the German, like a street bully, could pick a fight and then break it off against the P-38. He couldn’t do that with a P-51."

Heiden's general statement doesn't mention operational altitude. Guppy's P-38 pilot quotes (from Corky Smith and Stan Richardson) are more specific, and both give the high-altitude advantage to the P-51, agreeing with Gerald Brown in that respect.

>You also state that in YOUR opinion, critical Mach is the reason the 8th AF abandoned the P-38. I don't buy that either. Although the compression problem was a factor, it was the other problems that the 8th complained about. Cold cockpits, engine problems, difficulty with maintenance, level of difficulty for the pilots, and the continual lack of planes and spare parts.

The problems you describe certainly played an important role in the 8th Air Force's disappointment with the P-38. However, both the P-47 and the P-51 had teething problems, too, but they were fixed without abandoning the aircraft.

The reason I'm convinced critical Mach number was the decisive factor is that its problems were considered insurmountable by the 8th Air Force's leadership (according to an 1996 USAF research paper by LtCol Daneu). The problems you have described could have been fixed - in fact, it's a central point of your argument that they could! - but the low critical Mach number would have required the design of a completely new airframe.

Regards,

Henning (HoHun)

>12-07-2001 12:47 AM

[Guppy]

I don't see any major contradiction in Heiden's statement.

The main reason German fighters could escape at will was that the P-38s didn't pursue. That was because the pilots weren't confident they could recover from a dive, not because the Germans had a higher maximum dive speed and would eventually outdistance them.

With the dive flaps, the P-38s could pursue and break off the chase if they got into compressibility trouble. Obviously, the German fighter would pull ahead in the end. But if the P-38 was locked on his tail already, it might well stay there long enough to get the telling burst in--and if the German levelled off too soon, confident that he'd shaken off pursuit (as he would with an early P-38), he would be in for a very big shock.

I'm pretty sure that's what Heiden meant--the Germans still had an advantage in the dive, but it was no longer a guaranteed escape.

(Against the P-51, of course, the diving pursuit could be maintained indefinitely, assuming no great strength disparity between the pilots.)

By the way, the L variants of the P-38 were the L-1 and L-5.

[Tac]

Originally posted by batdog:
Hehe..TAC is sneaky. The J is faster AND lighter as it doesnt have quite the fuel load of the L...


 xBAT

P.S. Yea a GREEN 38 would be nice.

Hehe, just wait till they put the second effect of the dive flaps on the 38 and you'll see how much of a difference they make.

The J is marginally faster, and it wont have the dive flaps, so it'll be a squeak to fly vs almost any plane if they just get on to diving away. Think about it... the L will be able to follow you in OR make you auger if you follow it on a high speed dive near the deck... so people WONT follow the WHITE 38 on dives. But they see a GREEN 38 , oh ho, dive dive dive!.

"The pilot was looking down at me as he eased
ahead and close above me into sure death, unless he could take violent evasive
action. He split-Sed and I followed him. He nearly got out of my sight because
the P38 high-speed compressibility problem kept me from staying with him in a
vertical dive. I stayed out of trouble by doing a vertical barrel roll to pull
several Gs and keep my speed under control."

BTW, this is something that all 38 pilots in the MA should know. Im horrified at the number of 38s diving from 20k to 4 ft under because they dont pull g's on the dive.


 

[ 12-08-2001: Message edited by: Tac ]

[bolillo_loco]

Hi Hohun, I could not disagree with you or grippen more. If you have the pilots manual look at the section for diving. It clearly states that mach .675/.68 is the placarded limit with out dive flaps and that with the dive flaps extended it may be exceeded by 20 mph. It also states that trimming is not neccesary nor recomended, remember the P-38 unlike all other single engined a/c did not need to be trimmed and re-trimmed for speed changes. dive flaps made recovery much easier and efforless even for green pilots. read the above attachment that somebody else posted earlier. it looks like an official document to me. I agree that w/o dive recovery flaps, only experienced pilots like tony levier and other calm pilots could bring a 38 out of a dive at high speed, but again with flaps the plane recovers by itself.

Americacs hundred thousand states that several pilots flew the 38 with dive flaps and all were very pleased with the results, "recovery is effortless" it also goes on to say that dispite this most ranked it last in dive control and dive stability. I tend to agree with what most of renegade savage (but not all) says. I feel that the rumor mill resulting from failures of the 38H followed the 38 thru all its models, dispite fixes that brought the 38 up to par or did away with the problem all together. If you look at all the complaints on the P-38, unreliable engines, one generator, run away props, turbo regulator problems, cold cockpits, dive stability, slow rate of roll at medium to high speed, power restrictions at altitudes over 20,000ft, the P-38J-25-LO
(some of these problems were fixed with the first introduction of the 38J-5-LO) and
later models either solved the problem completely or brought it up to par with other a/c.

The test were the 38 with dive recovery flaps was tested against the P-47D in a dive levier stayed with the 47 or only lagged behind by a bit and then pulled right aside of the 47 after the dive shows that the dive recovery flaps broght it up to par with most a/c. P-47s also had dive recovery problems. late D models were fitted with dive recovery flaps. Levier stated that he was good friends with the P-47 pilot who is considered to be an expert on the 47 type, stated that after the last dive when the 47 really poured it on the P-47 pilot was beat black and blue between the thighs by the stick because it was thrashing about wildly in the cockpit.

The tests where P-47s, spitfires, and P-51s were all dove well beyond mach .8 seem to all have had special preperation. The P-47 for example had a specialy fitted propeller because in high speed dives no matter how sound the airframe is the propeller becomes the limiting factor. I have seen the high mach number dives for the mustang. they had the propeller completely removed for this dive and other special preperations were done. The mustang is well known for structural weakness when flown at full weight. it is designed for +8 g max at 8,000 lbs, this is 2,500 lbs heavier than the B/C/and D model. americas hundred points out the test where the P-51 was damaged as a result of the pull out from a mach.81 dive and the mustang had to be scrapped. Roger Freemans book points out several of the mustangs airframe weaknesses where several 51s had to be scrapped due to structural failures because of pull outs from high speed dives.

I could not agree more that the 38 was far to complex and one had to know a lot about it. I think as a result of this the rumor mill and green pilots and many people today just lable it as laim and maybe do not want to do research beyond that.

Thanks for the debate guys.

[ 12-08-2001: Message edited by: bolillo_loco ]

[HoHun]

Hi Hilts,

>All though they could not prove that it didn't work, the USAAF did not like 64" of manifold pressure on the Allison and did not specify it. However, Lockheed and Allison did several tests and it worked.

I'm sure the USAAF had well-defined criteria for acceptance of an engine setting, including bench run reliability tests.

I think to find out about the reasons for the USAAF not adopting the 64" Hg power setting, we'd have to determine the USAAF requirements and whether Lockheed or Allison actually met them.

For example, the 64" Hg setting might have worked in practice, and even worked reliably, but still the USAAF never formally approved of it. If the reason was that the manufacturer never proved the engine setting according to the USAAF criteria, the contradicting performance figures we're finding everywhere would seem unavoidable.

Then, the next question should be: Why was the power setting never formally approved of?

Regards,

Henning (HoHun)

[gripen]

Well, this has became far too long discussion. Anyway, couple comments more  

Generally I believe all pilots comments, but those tend to be so contradictory that it is pretty difficult to say something surely based on them; pilots tend to favour planes they liked most and comparison specially with enemy planes is difficult because skill of the pilot vary a lot. By collecting enough pilot's comments and pickingup just those which support your argument, you can "prove" what you want. A good example of this is the Bf 109 out turning Spitfire stories and in this discussion I see similar phenomena.

I hope that everyone interested about diving qualities of the P-38 download that NACA document I pointed to bolillo_loco. Document explains pretty well how dive recovery flaps worked and how pitching moment changed at various mach number. Also it should be noted that above mach 0.7 the pilot was more or less a passenger in his plane even with dive flaps,  Tony Levier wrote that the plane acted like a mad demon at compressebility speeds. The dive flaps added a lot of drag to keep the plane out dangerous speeds and made safe pull out possible at faster speeds than without them. But as the manual notes anything more than 45 degrees in dive at high altitude was not safe even with flaps.

I collected data about weights (AHT) at various combat loads (I wonder where from that bollilo_locos 10500lbs comes or is it 5500lbs?) and safe loading factors of the P-51 assuming safety factor 1,5 and linear estimates for loadings (which actually is not the right way but good enough here):

P-51A 8000 lbs 8.0g
P-51B no fuselage tank 9077 lbs 7.27g
P-51B fuselage tank empty 9332 lbs 6.89g
P-51B fuselage tank full 9842 lbs 6.46g
P-51D fuselage tank empty 9698 lbs 6.58g
P-51D fuselage tank full 10208 lbs 6.16g (AHT 6.3g my estimates are conservative)
P-51D 220 gallon external fuel 11708 lbs 5g

Assuming that in combat fuselage tank is at least near empty, we can see that safe g load factor is more than 6.5 (breaking load factor 9.75). Generally load factors above 6g were rare in combat except accidentally for example in the case of the stick force reversal (too much fuel in the fuselage tank). Borsodi trimmed his plane nose heavy and was able to pull out without over stressing his plane.

gripen

[bolillo_loco]

Hi grippen, I just meant to say about 2,500 lbs lighter, thank you for correcting me 10,200lbs sound quite correct. I moved back from texas last month and I lost my books   now I must replace them.

I could be wrong when I say this, but I feel that people believe that the P-38 was the only plane that became unsafe at speeds beyond mach .7 with or with out flaps. I had two books which stated mach .675 buffet began and at mach .74 nose dive tendency became termanal. this is with out dive recovery flaps. the flaps added some more speed to the dive, however I do not believe it was anything great in terms of speed. it looks like mach .05 perhaps, but nothing more.

the P-51, P-47, corsair, fw-190D, bf-109 series all were probably pretty unsafe at airspeeds beyond mach .75. from what I have read it seems to be so. even the mustang with its laminar airfoil it is highly cautioned in all pilots manuals not to exceed mach .75. beyond that the a/c is no longer safe and compressablility begins by the plane starting to become uncontrollable. the problem I see with the 38 is that in the initial push over from 30,000ft at a low to medium ias the a/c is going to pick up speed much more rapidly than a mustang and that is why it is so critical to be careful in the 38 w/o flaps. with flaps if compression is hit and the a/c is no longer in control the flaps atleast make recovery possible when it hits lower altitude. before this the pilot and plane were lost. this sounds familiar to all a/c I have mentioned above. 47's and 51's were all lost to compression and any of the american types that could reach or exceed 400 mph ias at 30,000 would all dive straight into the ground if they were power dove from 30,000 ft and 400 mph ias. if you dont believe me go and look at the P-47 training film at zenos warbird videos on high alt maneouvering in the 47. it lists the altitude needed to recover from a dive started at different speeds tas. from 30 k and at 400 mph tas the 47 will go straight into the ground. if you have americas hundred thousand go to the part on the 47 on pilots comments. one pilot resorted to firing all guns in an attempt to slow down his a/c  because his a/c refused to respond due to compression in a high speed dive. it wasnt until he rode the plane all the way to the deck as a passenger not a pilot that the plane did respond.

all the 400 mph + tas high performance a/c flying in ww 2 battle trim (ie no special attention for a special test to make it dive better) will crash into the ground when begining a  power dive from high ias at 30,000 ft.

thanks for the info grippen. going to get those books you listed as soon as I replace my others. and thanks for the debate it was interesting.

[gripen]

bolillo_loco,
Hm... I wonder where you have got a idea that the P-38 pick up speed much more rapidly than the Mustang at high altitude? Due to better propeller efficiency, exhaust thrust and lower drag the P-51 certainly accelerated better at high altitudes than the P-38. And yes, many P-47s and P-51s were lost due to comressebility (mostly because incorrect use of trim or stick force reversal), but if a pilot knew what to do, he could start dive from high altitude at high speed, enter compressebility speeds and recover safe. At least my copy of AHT does not support your argument nor other sources I have.

gripen

[bolillo_loco]

[HoHun]

Hi Hilts,

>The data and charts came from the Lockheed Martin archives. As I stated above, this was provided by a source currently employed by Lockheed Martin, to C.C. Jordan, and Warren Bodie was until the early to mid eighties, an engineer at Lockheed. Whether it is published in your favorite book or not is irrelevant.

It still would be nice to see the orginal data or charts, not only because they'd be more credible than a footnote in a secondary source, but also because they usually specify the exact circumstances with greater accuracy than secondary sources do.

Regards,

Henning (HoHun)

[HoHun]

Hi Guppy,

>Definitely the case. 4th FS (52nd FG) Spitfire pilots in February 1944 reported two encounters with four-ships of inline Fw 190s over Nice harbour in the Mediterranean.

Yes, that's exactly the kind of effect I was thinking of! I really wonder how Allied intelligence found out about the long-nose Focke-Wulf so early - many months before the type was actually finalized for production.

>One possibility which would allow for Galland actually flying a long-nosed 190 might be the pre-production service test models, which were around in early 1944.

Good suggestion! Since the fate of every Fw 190 prototype has been published since then, this might be verifiable. (I checked it once for the date orginally attributed to Lowell's story, and there was no armed Dora prototype available at that time.)

Regards,

Henning (HoHun)

[HoHun]

Hi Seeker,

>Ïf it's accepted that *type* could be seen at relativly long raange (Spit/Fw/P38) bit *marque* was hard to see, what implications does that have for an icon system?

Air Warrior, which just was closed, had a complete variant desctiption in the icon, Warbirds just had the general type.

This does have tactical implications as aircraft of different variants can have very different capabilities - to stay on topic, let me point out that P-38F versus P-38J is one of the best examples :-) -, and as you'd recognize newbies easily as they'd be bringing obsolete variants to fight.

Though you'd have to rely on visual recognition to discern the aircraft subtypes, which due to the lack of visual detail was only possible by the paint schemes, in some cases the paint schemes were so different that you'd know at a glance what you'd be facing - the P-38F was olive drab overall, the P-38J natural metal.

Still, I liked the general type icons better than the exact subvariant icons.

Regards,

Henning (HoHun)

[Seeker]

My point exactly, HoHun.

In fact, most of the books I've got on American A/C show that by 44 at least, any Jug, Stang or 38 you met, unless brand new, was very likely to be a patch work of colours as holes were patched, things were fixed and bits added from any thing an enterprising crew chief could find.

The point being you should have a way of saying "38!" from five miles away (I can recognise a Spit from inside a train carriage over five miles away - did it this summer), but I really don't believe you can tell _which_ 38 further than 1000 yrds.

It would be nice to have differeing marques of 38 in the game. I'd prefer not to have a bill board saying which one it was hanging over my head.